window.addEventListener('load', function () {
    let xian = document.querySelectorAll('.nav li');
    console.log(xian);   

    for (let i = 0; i < xian.length; i++) {
        xian[i].addEventListener('mouseover', function () {
            xian[i].style.borderBottom = ('2px solid white')
            xian[i].addEventListener('mouseout', function () {
                xian[i].style.borderBottom = ('none')
            })
        })
    }








})